Polarizing plates used in the related have a stacked structure in which protective films are attached to both surfaces of a polarizer formed of a polyvinyl alcohol (hereinafter, referred to as ‘PVA’)-based resin generally dyed with a dichroic dye or iodine, using an adhesive. However, in order to reduce the thickness of polarizing plates in line with the recent trend for reducing the size of display devices, single-sided polarizing plates, in which a protective film is only provided on one surface of a polarizer and a bonding layer is directly formed on the other surface of the polarizer without a protective film, have been developed. In the case of such single-sided polarizing plates in which a bonding layer is directly formed on a polarizer, however, polarizers may be easily cracked in severe conditions due to poor durability, and curling caused due to a difference in shrinkage rates between a protective film and a bonding layer may lead to light leakage in the case that single-sided polarizing plates are disposed in display devices.
To address these problems, techniques for forming a protective layer between a polarizer and a bonding layer by using a curable resin have been proposed. Korean Patent Application Laid-open Publication No.: 2011-0014555 discloses a polarizing plate including a protective layer formed between a polarizer and a bonding layer and having a tensile modulus of 100 MPa or above. In the disclosed polarizing plate, however, an epoxy-based resin or a hydroxyethyl acrylate-based resin used as a protective layer former has poor water resistance and a low glass transition temperature, and thus the durability and optical characteristics of the polarizing plate may be deteriorated in high-humidity, high-temperature environments.